This invention relates in general to communication systems, and more specifically to a method and apparatus for adapting antenna visibility for communications units within wireless networks.
The traditional approach used for terrestrial wireless communication networks such as cellular networks consists of dividing the desired coverage area into a set of overlapping regions, where all of the subscribers within each region are served from a single transceiver known as a base station using a point-to-multipoint (PMP) or one-to-many approach. One of the problems with a PMP architecture is that it becomes more difficult to establish links directly between a given subscriber radio and the base station as the transmission carrier frequency increases, which poses a problem for future wireless networks since they are increasingly being deployed at higher carrier frequencies.
Other problems are the economic burdens associated with deploying a system since large costs are incurred during deployment of the infrastructure before any revenue can be raised to offset those expenses. Additionally there are extensive problems of coordination and planning and expense associated with expanding such systems. To avoid or address these problems to one extent or another, a new type of network architecture known as xe2x80x9cmeshxe2x80x9d architecture is being explored. Some systems are being proposed and deployed for providing relatively broadband packet data services to residential customers. Some fixed wireless systems or networks that are part PMP and part mesh network have been proposed and may be referred to as hybrid systems or networks. These systems may be initially deployed in part as PMP systems with each of the communications units in the PMP arrangement also acting as wireless network access points for clusters of communications units operating in a mesh network arrangement.
In a mesh architecture 100, such as depicted in FIG. 1, a multiplicity of communications units, A-C and E-G 101-105 and 109-113 are deployed, normally one or more per household or business and operate in an ad-hoc peer to peer fashion to establish links where possible and as required among each of a given units neighbors. For example unit A can establish links or paths 117, 119, 121 with, respectively units E, D, and B since as is typical the units employ an omni-directional antenna. Some units can employ a directional antenna 123 such as unit E and this limits their ability to see (establish links with) units that are not in the direction of their antenna and improves their ability to see units in the direction of the antenna. Unit D 107 operates as a hybrid unit. Unit D is coupled to a base station 117 using a PMP link or path preferably acting as a network access point and in a mesh mode for and with the other units. This mesh network at the end of a PMP link is often referred to as a cluster.
Each or many of the communications units have the ability to relay communications signals from an originating communications unit to a target unit when these communications units are not able to create a direct communication link or path from one to the other unit. Information that is being communicated may be relayed or handed from communications unit to communications unit until it reaches the intended destination or target unit. For example, if unit E wanted to communicate with unit F 111, information from unit E would be relayed by unit D to unit F. Note: that if the direct link from unit D to F were interrupted by a tree growing or new house being constructed, the inherent redundancy in the mesh architecture allows routing the information from unit D through unit C or unit G. In this fashion the infrastructure or backbone that is represented by the traditional base stations and supporting equipment is in a sense deployed as the system gains customers and begins to realize revenue.
However the mesh architecture or system can also experience problems. For example when only a few units have been deployed they may need to have high antenna visibility in order to reach another unit. However as the density of the communications units increases the degree or amount of interference for one unit caused by all other units also increases and this can significantly decrease system capacity. Suddenly the system or at least units in a mesh mode need lower antenna visibility.
To appreciate the problems caused by this interference lets review a typical way of initiating communication between communications units. It begins with the transmission of a xe2x80x9cRequest-to-sendxe2x80x9d (RTS) packet by the initiating unit. The RTS packet is typically received by all units within the transmission range of, or that can see, the initiating unit. The RTS packet notifies these units that the initiating unit would like to establish a communication link with a target unit whose identity is specified within the packet contents.
Upon successfully receiving this RTS packet, the target unit will respond with a xe2x80x9cClear-to-sendxe2x80x9d (CTS) packet that notifies the initiating radio that the target unit is ready to begin receiving transmissions from the initiating unit. The CTS packet also serves notice to the rest of the units in the area that the transmission medium has been reserved so that they can refrain from simultaneous transmissions that might interfere with the prearranged transmissions. Note that any relaying units and their neighbors will also be notified and will need to refrain from simultaneous communications. Because all other units in the area of the target unit, originating unit, and relaying units, if any, are forced to remain idle during the subsequent communications between the initiating and target units, system throughput can be severely diminished. Any desired transmissions by the idled units are delayed which can negatively effect overall user satisfaction.
As the number or density of communications units grows this problem must be addressed. Using directional antennas to limit the number of units that are interfered with or idled can help but that also creates problems. For example, if a unit wishes to communicate with another unit that is using a directional antenna this will not be possible unless or until the antenna points in the direction of the unit. Another approach is power control but that is sub-optimum since the degree to which the power can be lowered is limited due to the signal strength requirement at the intended receiver. The problem with these approaches is they do nothing to change or take advantage of fundamental propagation characteristics. Obviously better methods and apparatus for adapting antenna visibility are needed.